1. Field of the Invention
The invention relates to a device for the surveillance of the pressure of a vehicle tire including a pressure-sensitive device disposed at the vehicle wheel for monitoring the tire pressure, which includes a pressure inlet port, to which the tire pressure is applied, and which includes a pressure discharge port, which can be connected to the pressure inlet port of the device for surrveilance.
2. Brief Description of the Background of the Invention Including Prior Art
The German Patent DE-2,813,058 C2 teaches a related device. The device of this reference monitors the tire pressure with a pressure-sensitive device, where the pressure-sensitive device is disposed at the vehicle wheel. In case the tire pressure falls below a preset tire pressure value, the pressure-sensitive device generates an output signal at the pressure discharge port furnished as a signal pressure, which corresponds to the existing tire pressure. A set member of a signal transfer device is actuated with this signal pressure such that the set member performs a stroke. The signal transfer device is also disposed at the vehicle wheel. A sensor, disposed fixed relative to the axis, monitors the position of the set member and recognizes thereby a tire pressure, which is disposed below a preset tire pressure. A corresponding information of the sensor can then be fed via an evaluation circuit to a display device. The display device can, for example, be disposed in the driver cabin.
If the tire pressure is equal to or higher than the preset tire pressure, then no signal pressure is present at the pressure discharge port of the pressure-sensitive device based on the constructive features of the pressure-sensitive device of the German Patent DE-2,813,058 C2. Consequently, the set member of the signal transfer device is disposed in starting position in which no display signal occurs or, respectively, the sensor recognizes that the tire existing pressure is disposed below the preset tire set-point pressure, based on the spring-loading of the set member.
Alternatively, the set member can assume the above-recited non-indicating starting position, if, based on a markedly dropped tire pressure, the signal pressure, applied to the set member, has become so low that the force of a restoring spring directed opposite to the signal pressure and coordinated to the set member prevails. The device according to the German Patent DE-2,813,058 C2 therefore is associated with the disadvantage that the tire-pressure surveillance can only be reliably performed up to a certain minimum tire pressure, where the minimum value of the tire pressure level is determined substantially by the force of the restoring spring.
The German Patent No. 526,227 to Hubert Tastenhoye et al. teaches a device for indicating a decreasing gas pressure, in particular for air tires. The reference uses a structure which employs seals and valves and a spring 15' for a pressure level assertation. The reference employs a whistling signal for indicating the presence of a low pressure. Such a whistling signal is associated with the disadvantage that it may not be of sufficient intensity that it can be heard or, alternatively, that it causes too much of a disturbance.
The German Patent Application Laid Open DE-OS 2,816,397 to Erhard Kenk teaches a valve with an optical display device for indicating a pressure decrease in an air-filled tire. The reference employs a valve pipe 2 with one or several openings 3 and a sealing cylindrical membrane 5 placed on the vave pipe 2. The reference employs light-reflection ratios to observe changes in the tire pressure. No provision is made for the presence of a signal at a remote location relative to the tire, for example, in the driver cabin.
The German Patent Application Laid-Open DE-OS 2,650,444 to Edward Joseph Cook teaches a device for surveillance of the pressure in a vehicle tire. The reference teaches to employ an acoustic valve for air-filled tires with a valve casing, which is directly attached to the wheel or to the tire valve. The teaching of this reference with the sound generation again does not appear to be a safe and practical solution in cases where reliability of a safety action is required.
The German Patent Application Laid Open DE-OS 2,528,180 to Nikolaus Botsis teaches an air-chamber valve for air-filled tires. A display device 6 is screwed into a bore. A display pin 21 is pushed outward upon occurrence of a leak in the air chamber in case of entry of air into the interior of the neck port 27. No remote indication is illustrated in this reference.
The German Petit Patent DE-G 8,330,963.2 to Rainer Achterholt teaches a valve cap for air-filled tires. The structure employs a membrane 26 which is applied with a spring ring 28. In this case, however, the sealing of the membrane 26 is not perfect. The presence of such a membrane appears to be a possibility of reduced safety of the reference device.
The German Petit Patent DE-G 8,206,932.8 to Wolfgang Lubs teaches a surveillance device for filling quantities. An apparatus is shown which allows to test the level of the pressure present in an automobile tire. No continuous monitoring appears to be a feature of this reference structure.